An indium tin oxide (ITO) film is widely known as a transparent conductive film used as an electrode circuit, a pixel electrode or the like in a liquid crystal display. Among these indium tin oxide films, an indium tin oxide film which is in the polycrystalline state obtained by heating has a satisfactorily low resistance of about 200×10−6 Ω·cm. Thus, the film has low resistance and high light transmittance that are required for conductors for liquid crystal displays. For contact resistance when chip-on-glass (COG) is performed, the indium tin oxide film has excellent low connection resistance without causing any problems. In order to form a circuit or a pixel electrode by etching such an indium tin oxide film, strong acid etchants, such as a mixture of HCl and HNO3 and a mixture of HCl and H2SO4, are required. However, if indium tin oxide films are etched using such a strong acid as an etchant, the amount of side etching increases, leading to difficulty in precision working.
Furthermore, since liquid crystal displays have been increasingly miniaturized year by year, in sections other than electrodes or wiring composed of an indium tin oxide film, in which the resistance must be further decreased, wiring composed of copper has been used instead of the conventional wiring composed of chromium or tantalum. However, the above-mentioned strong acid etchants used for etching indium tin oxide films exhibit significantly high etching performance for copper wiring. Since indium tin oxide films and copper significantly differ in etching rate and the amount of side etching is large, the copper wiring may become disconnected if strong acids used for etching indium tin oxide films are used. Conversely, it is impossible to etch indium tin oxide films with diluted hydrochloric acid or organic acids which have low etching performance for copper wiring.
A technique is known in which indium tin oxide films in the amorphous state are obtained by a specific production method. The indium tin oxide film in the amorphous state is known to be capable of being etched using an organic acid. Indium tin oxide films in the amorphous state have such a disadvantage that they have a high contact resistance. If the indium tin oxide film is formed at room temperature, it tends to have a microcrystalline structure, and the resistance is increased to about 1,000×10−6 Ω·cm. Therefore, a problem arises in which satisfactory connection resistance may not be obtained.
Under such circumstances, as the transparent conductive film replacing indium tin oxide films, indium zinc oxide (IZO) films have attracted attention. The indium zinc oxide films are known as superior transparent conductive films suited for precision working since they exhibit a low resistance value at around 400×10−6 Ω·cm even if formed at room temperature, have light transmittance almost equal to that of indium tin oxide films, can be etched with a weak acid, and the amount of side etching is small when etching is conducted with a weak acid. Furthermore, if indium zinc oxide films are used, dilute hydrochloric acid can be selected as an etchant which does not erode copper wiring. By using dilute hydrochloric acid, precision working can be achieved even if a circuit structure combining an indium zinc oxide film and copper wiring is used.
However, if the indium zinc oxide film is used as wiring for the above-mentioned liquid crystal display, and the wiring is COG connected, the connection resistance increases, giving rise to a problem when wiring in liquid crystal displays is further miniaturized. In addition, if indium zinc oxide films are stored in air, contact resistance may increase with the passage of time.
However, when the indium zinc oxide film is used for TCP (tape carrier package) connection, problems similar to those mentioned above may occur. To solve these problems, a transparent conductive film formed of indium tin zinc oxide is proposed in Patent document 1.
Patent document 1: JP-A-2001-155549
The invention has been made in view of the above problems, and an object thereof is to provide a transparent conductive film which can be fine etched using weak acids, has a low connection resistance, and superior light transmittance, of which the resistance can also be low when COG connection is performed, and the resistance does not vary with the passage of time.
Another object of the invention is to provide a substrate an electronic device, and a liquid crystal display, provided with the above-mentioned transparent conductive film.
Still another object of the invention is to provide a method for producing the above-mentioned substrate.